Originally Posted by MSPeconomist

My understanding is that if a SkyMiles member is with you on the same PNR and no one else is on the same PNR, then you clear together at the 24 hour, really after 5pm ATL time, window. If you want to upgrade a companion not on the same PNR, you request it by phone or whatever, but you clear separately in your own window if available.

Linking the PNRs is not equivalent to requesting a companion upgrade; these are separate issues.